Production method for semiconductor device

ABSTRACT

An object of the present invention is to provide a method of producing a Group III nitride semiconductor device having a chip form which is pentagonal or more highly polygonal maintaining good area efficiency and at a low cost. 
     The inventive method of producing a Group III nitride semiconductor device having a chip shape which is a pentagonal or more highly polygonal shape comprises a first step of epitaxially growing a Group III nitride semiconductor on a substrate to form a semiconductor wafer; a second step of irradiating said semiconductor wafer with a laser beam to form separation grooves; a third step of grinding and/or polishing the main surface side differently from the epitaxially grown main surface of the substrate; and a fourth step of division into individual chips by applying stress to said separation grooves.

CROSS REFERENCE TO RELATED APPLICATION

This application is an application filed under 35 U.S.C. §111 (a)claiming benefit, pursuant to 35 U.S.C. §119 (e) (1), of the filing dateof the Provisional Application No. 60/618,583 filed on Oct. 15, 2004,pursuant to 35 U.S.C. §111 (b).

TECHNICAL FIELD

The present invention relates to a method of producing a semiconductordevice. More specifically, the invention relates to a method ofproducing a semiconductor chip having a pentagonal or more highlypolygonal chip form (hereinafter referred to as “polygonal chip”).

BACKGROUND ART

A step of producing semiconductor devices by cutting a Group III nitridesemiconductor wafer having an n-type layer, an active layer and a p-typelayer stacked on an insulating substrate such as sapphire into chips,includes a step of forming separation grooves in a chip form by exposingthe n-type layer to etching, a step of polishing the substrate todecrease its thickness, a step of exposing the substrate by introducingthe diamond blade of a dicing saw into the separation grooves, a step offorming a scribe line along the trace for dicing by using a diamondblade of a scriber, and a step of obtaining chips by pushing anddividing the substrate, as disclosed in, for example, Japanese PatentApplication Laid-Open {kokai) No. 5-343742.

Japanese Patent Application Laid-Open (kokai) No. 11-354841 discloses astep of cutting and separating, including a step of forming separationgrooves in a chip form by exposing the n-type layer by etching, a stepof polishing the substrate to decrease its thickness, a step of exposingthe substrate by introducing the diamond blade of a dicing saw into theseparation grooves, a step of forming a scribe line from the backsurface side of the substrate at a position corresponding to the dicingline by using a scriber, and a step of obtaining chips by pushing anddividing the substrate.

It has been described that the sapphire substrate and the Group IIInitride semiconductor layer are hard and cannot be divided into chips bycleavage unlike GaAs and GaP and, hence, the thickness of the substratemust have been decreased, before dividing it into chips, so as to makeit more easily divided, and that stress-concentrating portions must beformed for dividing, or that dicing or scribing is necessary to locallydecrease the thickness to accomplish the division at desired positions.The diamond blade of the dicing saw is usually in the shape of a diskwhich is dedicated to linear machining, and is not capable of effectingpolygonal machining or curved machining. Even a method of forming amarking-off line on the Group III nitride semiconductor layer or on asapphire substrate, by a dicing saw with a diamond blade, issubstantially linear machining because the work to be machined has ahardness comparable to the hardness of the machining material, and it isdifficult to accurately form a marking-off line in the form of apolygonal line or in the form of a curve. Therefore, the chip form ofthe conventional Group III nitride semiconductor device was of a squareform.

In the Group III nitride semiconductor light-emitting device, on theother hand, light emitted from the active layer travels to go out of theGroup III nitride semiconductor light-emitting device but cannot go outfrom the surface of the chip due to the relationship of the refractiveindex and the light is reflected and is absorbed by the Group IIInitride semiconductor, by the sapphire substrate or by the electrodemetal, and is converted into heat. The ratio of light going out of thechip is called light extraction efficiency. The light extractionefficiency at the end of the chip is greater when the chip is of apolygonal form than when it is of a square form, and becomes a maximumwhen the chip is of a circular form. This is because the conditions forperpendicular incidence on the end surfaces from the center of the chipconsist of four conditions in the case of a square form, six conditionsin the case of a hexagonal form and perpendicular incidence is permittedunder every condition of 360 degrees in the case of a circular form.Therefore, the light extraction efficiency on the end surfaces of thechip can be improved in the case of the hexagonal chip as compared tothe square chip.

Japanese Patent Application Laid-Open (kokai) No. 9-082587 discloses amethod of producing a hexagonal chip by using a conventional machiningtechnology. Referring to FIG. 4 of this patent document, the chips aredivided by forming separation grooves which are linear machining linesin a manner that triangles and hexagons neighbor each other. That is,triangular portions are rounded off to obtain hexagonal chips. JapanesePatent Application Laid-Open {kokai) No. 2000-164930 discloses thearrangement of electrodes of the Group III nitride semiconductorlight-emitting device of a hexagonal form. However, this patent documentis quite silent about the method of producing the hexagonal chip.

In recent years, there has been developed a device for formingseparation grooves for cutting chips by using a laser beam as disclosedin, for example, U.S. Pat. No. 6,413,839. The laser beam can be used notonly to simply substitute for the conventionally employed dicing saw orthe scriber but also is a machining technology that offers unknownprobability which may realize a machining method that could not beaccomplished by conventional methods. For example, Japanese PatentApplication Laid-Open {kokai) No. 10-044139 discloses a technology forcutting by irradiating the bottoms of the separation grooves that havebeen formed in advance with a laser beam to cause a local thermalexpansion. The laser beam is not only the heating means but also iscapable of forming separation grooves having any depth or width bycontrolling the diameter of the beam, position of the focal pointthereof, laser output and irradiation time. As an example, JapanesePatent Application Laid-Open {kokai) No. 11-163403 discloses atechnology for forming separation grooves in the surface of the sideopposite to the surface irradiated with the laser beam.

A polygonal chip has a number of sides greater than that of theconventional square chips and, hence, for example, a light-emittingdevice features an improved light extraction efficiency at the endsurfaces of the chip. According to the conventional method of producinga hexagonal chip as described above, a triangular chip and a hexagonalchip are obtained by linearly forming the machining lines by using adicing saw or by a scribing method. According to this method, however,the areas of the triangular shape are lost, and the area efficiencybecomes poor. The light-emitting device of a polygonal chip can beexpected to provide a high brightness. According to the conventionalmethod of machining the polygonal chip, however, a problem remains inregard to a large machining loss and a poor area efficiency.

According to a laser machining method, a Group III nitride semiconductoror sapphire substrate is removed from the semiconductor surface side orthe sapphire substrate side of the Group III nitride semiconductordevice by sublimation from a portion irradiated with a laser beam whichhas a beam diameter of an order of microns, and there can be formedseparation grooves which are deeper and narrower than that formed by thedicing method within short periods of time. However, if the substratebeing machined is warping, the position of focal point of the laser beamundergoes a relative change, and the width and depth of the separationgroove vary. A method can be contrived to control the position of thefocal point to meet the warping by measuring the warping of thesubstrate in advance. In many cases, however, the shape of warpingvaries as the machining by laser proceeds, and a machining precision isnot obtained for forming separation grooves of the order of microns inthe whole surface of the substrate. To accomplish the laser machiningmaintaining high precision, therefore, the warping of the sapphiresubstrate to be machined must be decreased.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a method ofproducing a Group III nitride semiconductor device, having a chip formwhich is pentagonal or more highly polygonal, to solve theabove-mentioned problems and maintain good area efficiency and at a lowcost.

The present inventors have keenly endeavored to solve the above problemsand have arrived at the present invention. Namely, the present inventionprovides the following:

1. A method of producing a Group III nitride semiconductor device havinga chip shape which is a pentagonal or more highly polygonal shape,comprising a first step of epitaxially growing a Group III nitridesemiconductor on a substrate to form a semiconductor wafer; a secondstep of irradiating said semiconductor wafer with a laser beam to formseparation grooves; a third step of grinding and/or polishing the mainsurface side different from the epitaxially grown main surface of thesubstrate; and a fourth step of division into individual chips byapplying a stress to said separation grooves.

2. A method of producing a Group III nitride semiconductor deviceaccording to 1 above, wherein the first step, the second step, the thirdstep and the fourth step are included in this order.

3. A method of producing a Group III nitride semiconductor deviceaccording to 1 or 2 above, further including a fifth step of formingtrenches, in which at least the n-type layer is exposed, correspondingto the positions for forming the separation grooves.

4. A method of producing a Group III nitride semiconductor deviceaccording to 3 above, wherein the fifth step exists before the secondstep.

5. A method of producing a Group III nitride semiconductor deviceaccording to 3 above, wherein the fifth step exists after the secondstep.

6. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 5 above, wherein the second step irradiatesa laser beam from the semiconductor side of the semiconductor wafer.

7. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 6 above, wherein the separation grooves atleast partly reach the substrate.

8. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 7 above, wherein the second step irradiatesa laser beam from the substrate side of the semiconductor wafer.

9. A method of producing a Group III nitride semiconductor deviceaccording to 8 above, wherein the second step comprises a step ofirradiating a laser beam from the semiconductor side of thesemiconductor wafer and a step of irradiating a laser beam from thesubstrate side of the semiconductor wafer.

10. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 9 above, wherein the separation grooveshave a V-shape in cross section.

11. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 10 above, wherein the second step forms aseparation groove of the form of a polygonal line that is bent, forms aplurality of separation grooves, of the form of a polygonal line that isbent, in a form of being translated in parallel and, then, forms linearseparation grooves by connecting every other bending point of theneighboring separation grooves in the form of a polygonal line.

12. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 10 above, wherein the second step formsfirst separation grooves of the form of a broken line, forms secondseparation grooves of the form of a broken line that intersect the firstseparation grooves of the form of the broken line at a first angle, andforms third separation grooves of the form of a broken line thatintersect the second separation grooves of the form of the broken lineat a second angle and further intersect the first separation grooves ofthe form of the broken line at a third angle, the sum of the firstangle, the second angle and the third angle being 180 degrees.

13. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 12 above, wherein the semiconductor waferis ground and/or polished at the third step to be not thicker than 150μm.

14. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 13 above, wherein the fourth step isexecuted by pushing the substrate onto a spherical metal mold.

15. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 14 above, wherein the chip shape issubstantially an orthohexagonal shape.

16. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 14 above, wherein the chip shape issubstantially a pentagonal shape.

17. A method of producing a Group III nitride semiconductor deviceaccording to 16 above, wherein the second step forms separation groovesof a hexagonal shape by forming separation grooves of the form of apolygonal line that is bent, forming separation grooves of the form of aplurality of polygonal lines that are bent in a form of being translatedin parallel and, then, forming linear separation grooves by connectingevery other bending point of the neighboring separation grooves of theform of polygonal lines and, further, forms linear separation groovesconnecting the opposing two sides of the separation grooves of saidhexagonal form.

18. A method of producing a Group III nitride semiconductor deviceaccording to 16 above, wherein the second step forms separation groovesof the form of a hexagonal shape by forming first separation grooves ofthe form of a broken line, forming second separation grooves of the formof a broken line that intersect the first separation grooves of the formof the broken line at a first angle, and forming third separationgrooves of the form of a broken line that intersect the secondseparation grooves of the form of the broken line at a second angle and,further, intersect the first separation grooves of the form of thebroken line at a third angle, the sum of the first angle, the secondangle and the third angle being 180 degrees and, further, forms linearseparation grooves connecting the opposing two sides of the separationgrooves of said hexagonal form.

19. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 10, 13 and 14 above, wherein the chip issubstantially of a circular form.

20. A method of producing a Group III nitride semiconductor deviceaccording to any one of 1 to 19 above, wherein the Group III nitridesemiconductor device is a light-emitting device.

21. A method of producing a Group III nitride semiconductor deviceaccording to 20 above, wherein the first step forms the semiconductorwafer by epitaxially growing an n-type layer, a light-emitting layer anda p-type layer comprising the Group III nitride semiconductor in thisorder on the substrate.

22. A Group III nitride semiconductor light-emitting device produced bya production method of 20 or 21 above.

23. A lamp comprising a light-emitting device of 22 above.

24. A lamp according to 23 above, wherein a light energy conversionmaterial is arranged more at the end portion than at the center of asemiconductor chip forming a light-emitting device.

The present invention makes it possible to obtain a semiconductorlight-emitting device having a chip form which is pentagonal or morehighly polygonal and, particularly, a group III nitride semiconductorlight-emitting device featuring excellent light extraction efficiency onthe end surfaces of the chip and maintaining a good area efficiency overthe whole semiconductor wafer surfaces at a low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a procedure for forming separationgrooves of hexagonal chips.

FIG. 2 is another diagram illustrating a procedure for formingseparation grooves of hexagonal chips.

FIG. 3 is a diagram illustrating a procedure for forming separationgrooves of pentagonal chips.

FIG. 4 is another diagram illustrating a procedure for formingseparation grooves of hexagonal chips.

FIG. 5 is a plan view of a light-emitting device fabricated in Example1.

FIG. 6 is a plan view of a light-emitting device fabricated in Example7.

FIG. 7 is a plan view of a light-emitting device fabricated in Example8.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will now be described concerning chiefly a semiconductorlight-emitting device, though the invention is in no way limitedthereto.

In the present invention, there is no particular limitation on thepentagonal or more highly polygonal form if it has 5 or more corners.The polygonal form includes, for example, the ones having 5 to 10corners. Even a circle which is the ultimate polygon is included in thepolygonal form having 5 or more corners of the present invention.

Among the polygonal chips having a good light extraction efficiency atthe ends of the chip as compared to the conventional square chips, theform which permits the least machining loss is a hexagonal chip form ofhoneycomb-shaped separation grooves for dividing the chips in thesurface of the semiconductor wafer or in the surface of the substrate. Apentagonal chip obtained by further adding a separation groove so as todivide the hexagonal chip into two, too, has a decreased machining lossthough the light extraction efficiency drops to some extent. A circularchip that can be put into practice by the invention has a largemachining loss but has a maximum light extraction efficiency on the endsurfaces of the chip.

In the first step of the invention, it is desired to use a sapphiresubstrate or an SiC substrate for growing the Group III nitridesemiconductor. As the substrate, there can be further used a glasssubstrate, an oxide substrate such as MgAl₂O₄, ZnO, LiAlO₂, LiGaO₂ orMgO, a silicon substrate, a GaAs substrate and a GaN substrate withoutany limitation. Examples appearing later deal with a sapphire substratehaving a very weak cleaving property. However, fabrication of apolygonal chip by using a substrate having a strong cleaving property,such as a silicon substrate or a GaAs substrate, requires cutting evenin a direction of a weak cleaving property. Therefore, the presentinvention is effective in cutting such substrates, too.

For example, a semiconductor wafer is obtained by epitaxially growing ann-type layer, a light-emitting layer and a p-type layer by the MOCVDmethod on the substrate via, usually, a buffer layer. The buffer layeris not often needed depending upon the substrate that is used and theconditions for growing the epitaxial layer.

As the Group III nitride semiconductor constituting the n-type layer,light-emitting layer and p-type layer, there have been known many GroupIII nitride semiconductors represented by, for example, the formulaAl_(x)In_(y)Gai-_(x)-_(y)N (o≦x≦1, O≦y≦1, x+y≦1). In the presentinvention, too, there can be used the Group III nitride semiconductorsrepresented by the formula Al_(x)In_(y)Gai-_(x)-_(y)N (o≦x≦1, O≦y≦1,x+y≦1) inclusive of known compound semiconductors without anylimitation.

There is no particular limitation on the method of epitaxially growingthe Group III nitride semiconductor, and there can be employed any knownmethod such as MOCVD (organometal chemical vapor deposition), HVPE(hydride vapor growing method) and MBE (molecular ray epitaxial method).A preferred growing method is an MOCVD method from the standpoint ofcontrolling the film thickness and mass production. In the MOCVD method,the carrier gas may be hydrogen (H₂) or nitrogen (N₂), the Ga sourcewhich is a Group III starting material may be trimethylgallium (TMG) ortriethylgallium (TEG), the Al source may be trimethylaluminum (TMA) ortriethylaluminum (TEA), the In source may be trimethylindium (TMI) ortriethylindium (TEI), the N source which is a Group V starting materialmay be ammonia (NH₃) or hydrazine (N₂H₄). As for the dopants, there areused a monosilane (SiH₄) or a disilane (Si₂H₆) as the starting Simaterial and a german (GeH₄) or an oganogermanium compound as thestarting Ge material for the n-type, and a biscyclopentadienylmagnesium(Cp₂Mg) or a bisethylcyclopentadienylmagnesium ((EtCp)₂Mg) as thestarting Mg material for the p-type.

On the semiconductor wafer formed in the first step, an n-electrode anda p-electrode are further formed on an n-type layer and a p-type layer,respectively. The electrodes, however, may be formed after the end ofthe second step. There have been known n-electrodes and p-electrodes ofvarious compositions and structures, and the present invention may useany kinds of them inclusive of the known ones.

To form the surface for forming the n-electrode, the n-type layer isexposed by removing the p-type layer and the light-emitting layer by,for example, dry etching. At this moment, the positions for dividing thechips (i.e., the positions for forming the separation grooves), too, areetched to expose the n-type layer, and trenches that will be describedlater may be formed, simultaneously, by dry etching.

It is desired that the surface for forming the n-electrode is formed onone corner in the case of a hexagonal chip. The size of the n-electrodeis the same as that of the conventional square chip. The p-electrode maybe a light-transmitting electrode or a reflecting electrode. That is,the chip may be either of a face-up structure or a flip-chip structure.In the case of the light-transmitting electrode, it is desired that thebonding pad is formed on another corner facing the surface for formingthe n-electrode. The n-electrode forming surfaces may be formed at aplurality of corners, on the hexagonal sides extending the n-electrodeslike twigs, or may be formed along the sides. An insulating film such asa silicon oxide film may be formed on the surface of the chip to avoid ashort circuit between the n-electrode and the p-type layer or thep-electrode.

The semiconductor wafer formed through the first step is put through thesecond to fourth steps so as to be divided into individual chips.

In the second step, the semiconductor layer is irradiated with a laserbeam at a predetermined position (separation zones for division intoindividual chips) to form separation grooves of a depth which desirablyreaches the substrate. The separation grooves, however, need notnecessarily reach the substrate. This is not necessary particularly whenthe separation grooves are formed in the back surface of the substrate(surface on where no semiconductor is epitxially grown), too, as will bedescribed later.

There is no particular limitation on the width of the separation grooveif it can be held in the separation zone. When a trench that will bedescribed later has been formed in advance, the trench is irradiatedwith a laser beam to form a separation groove having a width narrowerthan that of the trench and having a depth which desirably reaches thesubstrate. The depth of the separation groove is desirably about 20 μmto about 50 μm though it may vary depending upon the thickness of thesubstrate after ground.

The separation grooves may have any shape in cross section but desirablyhave a V-shape. Upon forming the separation grooves of the V-shape,stress concentrates in the bottom portions of the separation groovesenabling the chips to be easily divided. Smooth and neat chip-dividingsurfaces are obtained when the separation grooves are formed with alaser beam. This is presumably due to a thermally affected portion beingformed from the bottoms of the separation grooves into the interior ofthe substrate facilitating the division of the chips. The depth of thethermally affected portions increases as the separation grooves areformed in a sharp V-shape with the laser beam.

The separation grooves can be formed on the back surface of thesubstrate by irradiating the back surface of the substrate (surfacewhere no semiconductor is epitaxially grown) with a laser beam. Theseparation grooves may be formed on either the semiconductor side or theback surface side of the substrate. When formed on both sides, however,division of the chips is facilitated and, besides, light is extracted inincreased amounts through the separation grooves to further improve thelight extraction efficiency. The shape of the separation grooves in theback surface of the substrate is, desirably, a V-shape but may be aU-shape instead.

The shape of the separation groove can be controlled by, for example,varying the focusing position of the laser beam. In general, when thefocusing position is separated, the width of the separation groove isbroadened to approach that of he U-shape. A multiplicity of laser beamsmay be irradiated to adjust the shape of the separation grooves.

The laser machining apparatus that can be used in the present inventionmay be of any type provided it is capable of forming separation groovesfor dividing the semiconductor wafer into the individual chips, and hasa computer-controlled stage for placing the semiconductor wafer.Concretely, there can be used a CO₂ layer, a YAG laser or an excimerlaser. The laser oscillation system may be either a continuousoscillation or a pulse oscillation. When the trench is irradiated with alaser beam from the side of the semiconductor layer, the beam must bemade as fine as possible. It is, therefore, desired that the apparatusis capable of emitting a fine beam.

The laser beam may have a wavelength of 355 nm or 266 nm, or may have afurther short wavelength. The frequency is, preferably, 1 to 100,000 Hzand, more preferably, 30,000 to 70,000 Hz. The output is, desirably, aminimum output necessary for obtaining desired separation grooves thoughit may vary depending upon the width and depth of the separationgrooves. An excess of laser output may cause thermal damage to thesubstrate and the compound semiconductor. Therefore, the above minimumoutput is, usually, not larger than 2 W and, more desirably, not largerthan 1 W.

The present invention can include a fifth step of forming, in advance,trenches for exposing the n-type layer at positions (separation zones)where the chips are to be divided, i.e., at positions where theseparation groove are formed. Upon forming the separation grooves in thetrenches by laser machining, the active layer and the p-type layer areprevented from being damaged by the laser machining, and a furtherpreferred embodiment is obtained as compared to when no trench isformed, in advance, at the positions where the chips are to beseparated. Conversely, the trenches may be formed after the separationgrooves are formed. In this case, there is obtained an advantage in thatthe contamination is removed from the side surfaces of the separationgrooves formed by the laser machining.

The trench is desirably formed by etching such as wet etching or dryetching. This is because the etching does not damage the surfaces andthe side surfaces of the compound semiconductor. The dry etching mayemploy such means as reactive ion etching, ion milling, focused beametching or ECR etching, and the wet etching may use a mixed acid of, forexample, sulfuric acid and phosphoric acid.

It is desired that the trenches have at least the n-type layer that isexposed, and can be simultaneously formed when the surface for formingthe n-electrode is exposed as described above since this enables thestep to be simplified. The trenches may have any shape in cross section,such as rectangular shape, U-shape or V-shape. However, the rectangularshape is desired for forming the separation grooves on the bottomsurface.

A method of scribing separation grooves so as to obtain a chip of apolygonal form, such as an orthohexagonal form comprises, as shown inFIG. 1, forming separation grooves of the form of a polygonal line by,first, irradiating a polygonal line (Al) having sides of the same lengthand having bending points bending at, for example, 120 degrees with alaser beam so as to traverse the semiconductor wafer. Thereafter,separation grooves are newly formed having the form of a polygonal line(A2) which is a parallel translation from the polygonal line (A1). Theparallel translation is repeated to form separation grooves of the formof the polygonal line over the whole surface of the semiconductor wafer.Referring next to FIG. 2, every other bending point of the polygonalline are selected and are connected to the bending points of theneighboring polygonal line that is translated in parallel thereby toform linear separation grooves (B). Thereafter, the bending points thatwere not selected are connected to the bending points of the neighboringpolygonal line translated in parallel to the side opposite to the abovepolygonal line that was translated in parallel, thereby to form linearseparation grooves (C). Thus, there are formed separation grooves of ahoneycomb hexagonal chip form on a semiconductor wafer. To obtain apentagonal chip, further, a linear separation groove may be furtherformed as represented by a straight line (D) in FIG. 3.

To obtain the hexagonal chip, further, there is a method of formingseparation grooves of an orthohexagonal shape by forming separationgrooves of the form of a broken line that are formed in three directionsby being turned by 60 degrees, respectively. This method is shown inFIG. 4. In a first direction, there are formed separation grooves (E) ofthe form of a broken line discretely forming the separation grooves likea broken line having a length same as the length of a side of thehexagonal chip form. Next, the stage is turned by 60 degrees. There areformed separation grooves (F) of the form of a broken line having thelength same as the length of a side of the hexagonal chip form startingfrom the ends of the separation grooves (E) of the form of a broken linein the first direction, thereby to form separation grooves of the formof a broken line in a second direction. Next, the stage is furtherturned by 60 degrees. There are formed separation grooves (G) of theform of a broken line having the length same as the length of a side ofthe hexagonal chip form starting from the ends of the separation grooves(F) of the form of a broken line in the second direction, thereby toform separation grooves of the form of a broken line in a thirddirection. Thus, there are formed separation grooves for obtaininghoneycomb hexagonal chip forms on the semiconductor wafer. To obtain apentagonal chip, a linear separation groove may be further formed asrepresented by a straight line (D) in FIG. 3. The procedure for formingthe separation grooves for obtaining the honeycomb hexagonal chip formis not limited to the above-mentioned procedure or method only. Further,the form need not necessarily be an orthohexagonal form but may be anyhexagonal form by varying the angle of the polygonal line or by varyingthe rotational angle of the broken lines in three directions.

If these complex groove forms are not precisely applied to the wholesemiconductor wafer, the depth of separation grooves and the width ofseparation grooves partly undergo variation causing the occurrence ofsuch defects as cutting-away and scars when divided into chips. Toscribe the separation grooves maintaining good precision on the wholesemiconductor wafer, it is necessary to decrease the warping of thesemiconductor wafer to maintain constant as much as possible thefocusing of the laser beam relative to the surface of the wafer over thewhole wafer. A method may be to utilize an automatic focusing positioncontrol function that is incorporated in the laser machining apparatusitself. In many cases, however, the shape of warping varies as the lasermachining proceeds. Basically, therefore, it is important to minimizethe warping of the semiconductor wafer to be irradiated with a laserbeam. Upon forming the separation grooves by machining the semiconductorwafer free of warping with a laser beam, there are formed separationgrooves having stable widths and depths in the whole semiconductorwafer.

A semiconductor wafer epitaxially growing a thin film on the substrateis in many cases more warped than the substrate on which no film isepitaxially grown. The substrate having an increased thickness is warpedless after a film is epitaxially grown thereon. However, too large athickness drives up the cost. Therefore, to obtain a stable epitaxialfilm without developing warping during the epitaxial growing, thesubstrate, usually, should have a thickness of about 350 μm to about 450μm. When the effect of warping appears conspicuously due to a thickepitaxial film, there is often used a sapphire substrate having athickness which is further increased to about 600 μm. This, however,does not hold when the warping of the semiconductor wafer is controlledsuch as using a substrate of the same kind as the epitaxial filmdeposited on the upper side like a GaN substrate or using a substratethat has been warped in advance.

In the third step of the invention, it is desired that the back surfaceof the substrate having the above-mentioned thickness is ground and/orpolished to decrease the thickness of the semiconductor wafer to about150 μm. The smaller the final thickness after the grinding and/or thepolishing, the smaller the probability of causing scars to the endsurfaces of the chips when they are being divided and, further, makingit possible to obtain polygonal chips even without relying upon aspecial chip-dividing method. Conversely, when the final thickness ofthe semiconductor wafer becomes too small, the semiconductor wafer iswarped making it difficult to be divided into the chips and oftencausing the semiconductor wafer to be damaged when the back surface isbeing machined giving rise to the occurrence of a defect such ascracking. The thickness is desirably not larger than about 120 μm, moredesirably, not larger than about 100 μm and, further desirably, notlarger than about 85 μm. The lower limit is, preferably, not smallerthan about 40 μm and, more preferably, not smaller than about 60 μm.

When the substrate is ground and/or polished so as to be easily dividedinto the chips, the strength of the substrate is reduced and the warpingincreases. Therefore, this step of decreasing the thickness of thesemiconductor wafer by grinding and/or polishing the back surface sideof the substrate, is better effected after the step of forming theseparation grooves. When the separation grooves are to be formed in theback surface of the substrate, however, it is desired that the grindingis effected prior to forming the separation grooves from the standpointof maintaining precision. When the separation grooves are to be formedon both sides, i.e., on the semiconductor side of the semiconductorwafer and on the back surface side of the substrate, the separationgrooves are formed in the semiconductor side, first, followed by thegrinding and/or the polishing and, thereafter, the separation groovesare formed again in the back surface side of the substrate.

Further, if the separation grooves are formed having a depth reachingthe substrate, the warping of the semiconductor wafer as a whole can bedecreased, which is further desirable. This is because the thin filmwhich causes the warping is cut at the positions of the separationgrooves, and the stress which the thin film gives to the substrate iscut at the positions of the separation grooves, decreasing the stressthat warps the wafer. This not only decreases the defect of cracking ofthe semiconductor wafer in the step of grinding and/or polishing theback surface of the substrate after the step of forming the separationgrooves but also makes it possible to uniformly machine the whole backsurface of the substrate and, hence, to obtain a semiconductor waferhaving a uniform thickness.

When the thickness of the semiconductor wafer is not uniform, theneighboring chips irregularly rub each other at the time of dividinginto the chips because the separation grooves have bending points, andthere locally occur cuts and scars on the end surfaces of the chips.Therefore, the separation grooves scribed prior to the step ofdecreasing the thickness of the substrate should desirably have a depthreaching the substrate.

The back surface of the substrate may be ground and polished by anyknown method. Among them, it is desired to effect the grinding andpolishing by using abrasive particles such as diamond.

The step of division into individual chips is conducted by impartingstress by using rollers to the semiconductor wafer obtained through thefirst to third steps thereby to generate cracks from the separationgrooves through up to the interior of the substrate.

When the chips are of a square form, the chips can be divided by abreaker using a notch. In the case of a chip which is pentagonal or morehighly polygonal, however, use of a notch which exerts the stress ontothe linear region of the semiconductor wafer causes defects such ascutting-away to a large extent. Similarly, the dividing method whichlinearly scribes a polygonal line also causes defects such ascutting-away. Therefore, the semiconductor wafer to be divided intochips should desirably have a small thickness.

When the semiconductor wafer has a large thickness, it is desired thatthe chips are divided by placing the semiconductor wafer on a sphericalmetal mold which can divided the wafer into the individual chips in adirection in which the gap among the neighboring chips increase. Whenthe spherical metal mold is used, it is desired that the thickness ofthe semiconductor wafer is not smaller than about 90 μm but is notlarger than 150 μm and that the depth of the separation grooves is about15 μm to about 20 μm.

When the semiconductor wafer is thin, stress is imparted by usingrollers to generate cracks in the substrate so as to be divided intochips. When the semiconductor wafer has a thickness of not larger than100 μm and the separation grooves have a depth of not smaller than 15μm, stress is imparted by using rollers to divide the wafer into chips.To decrease the probability of defects such as scars, it is necessary tofurther increase the margin.

When the semiconductor wafer is thinner, division into chips can beaccomplished even by using a chip breaker using a notch. By optimizingthe shape of notch end of the chip breaker and the stress exerted on thenotch so that stress can be uniformly applied over a wide region likethe roller, division into chips can be accomplished by using the chipbreaker even when the semiconductor wafer has a thickness of about 100μm.

The thus obtained polygonal chip having five or more corners exhibitsbetter light extraction efficiency at the ends of the chip than theconventional square chips. A face-up type chip may be formed by adheringthe substrate side to the lead frame by using a silver paste or an epoxyresin and by bonding wires to both the positive and negative electrodes.Or, a flip-chip type chip may be formed by adhering both the positiveand negative electrodes to the lead frame via an electrically conductingmaterial such as solder. A lead frame mounting the chip can be moldedwith a resin to use it as a very bright blue or green lamp. Or, a lightenergy conversion material such as a fluorescent material may bearranged surrounding the chip to use it as a very bright white lamp. Inthis case, it is advantageous to arrange the light energy conversionmaterial in an amount larger near the ends than at the center of thechip to effectively utilize light emitted from the ends of the chip.Moreover, a variety of designs can be accomplished by taking intoconsideration the shape of the lead frame and the distribution of lightemitted from the lamp.

EXAMPLES

The invention will now be concretely described by way of Examples towhich, however, the invention is in no way limited.

Example 1

A blue light-emitting device comprising a Group III nitridesemiconductor having an orthohexagonal chip form was fabricated in amanner as described below. FIG. 5 is a plan view of a light-emittingdevice fabricated in this example, wherein reference numeral 1 denotes ap-electrode, 2 denotes a p-electrode bonding pad, 3 denotes an n-typeexposed surface and reference numeral 4 denotes an n-electrode.

A Group III nitride semiconductor stacked layer structure was formed bysuccessively stacking, on a sapphire substrate having a diameter of 5.1cm (2 inches) and a thickness of 420 μm and via a buffer layer of AlN,an underlying layer of undoped GaN having a thickness of about 4 μm, ann-side contact layer of Ge-doped (concentration of 1×10¹⁹/cm³) GaNhaving a thickness of about 2 μm, an n-side clad layer of Si-doped(concentration of about 1×10¹⁸/cm³) Ino.₁Gao.₉N having a thickness ofabout 12.5 nm, a light-emitting layer of a multiple quantum wellstructure, in which a barrier layer of GaN having a thickness of about16 nm and a well layer of In_(0.2)Ga_(0.8)N having a thickness of about2.5 nm were stacked five times alternately and finally the barrier layerwas further stacked, a p-side clad layer of Mg-doped (concentration of1×10²⁰/cm³) Alo.o₇Gao.₉₃N having a thickness of about 2.5 ran and ap-side contact layer of Mg-doped (concentration of 8×10¹⁹/cm³)Alo.o₂Gao.₉₈N having a thickness of about 0.16 μm by an MOCVD method.

On the p-side contact layer of the Group III nitride semiconductorstacked layer structure, there was formed a light-transmittingp-electrode having a structure of laminating a Pt layer and an Au layersuccessively from the side of the p-side contact layer on apredetermined position relying upon a photolithography technology and alift-off technology. Then, relying upon the photolithography technology,there was formed a p-electrode bonding pad having an Au/Ti/Al/Ti/Aulayer structure from the semiconductor side.

Next, relying upon the photolithography technology and the reactive ionetching technology, the n-side contact layer was exposed by etching, anda surface for forming n-electrode was formed in a semicircular shape byetching. Next, an n-electrode of a Cr/Ti/Au three-layer structure wasformed on the n-electrode forming surface by a method known to peopleskilled in the art.

The thus obtained Group III nitride semiconductor wafer was put to thestep of cutting. First, a water-soluble resist was uniformly applied byusing a spin coater onto the whole surface on the semiconductor layerside of the wafer, and was dried to form a protection film having athickness of about 0.2 μm so that contaminant due to the cutting willnot adhere onto the Group III nitride semiconductor layer at the time ofmachining with a laser.

Next, a UV tape was stuck to the sapphire substrate side of the waferand was fixed by a vacuum chuck onto a stage of a pulse laser machiningapparatus. The stage was of a rotary structure which was controlled by acomputer to move in the X-axis (right and left) and in the Y-axis (backand forth) directions. After being fixed to the vacuum chuck, a laseroptical system was so adjusted that the focal point of laser was on thesurface of the protection film, and separation grooves were formed bythe irradiation with a laser beam as shown in FIG. 1 so as to traversethe semiconductor wafer to, first, form a polygonal line (Al) having thesame length of sides with an angle of 120 degrees. Next, separationgrooves were formed to describe a polygonal line (A2) which was aparallel translation of the polygonal line (A1). This was repeated toform separation grooves of the form of the polygonal line over the wholesurface of the semiconductor wafer. Next, as shown in FIG. 2, everyother bending point of the polygonal line was selected and was connectedto a bending point of the neighboring polygonal line which was aparallel translation to form separation grooves as represented bystraight lines (B). Separation grooves were further formed asrepresented by straight lines (C) by connecting the bending points thatwere not selected to the bending points of a neighboring polygonal linemoved in parallel toward the opposite side. Thus, there were formedseparation grooves of a honeycomb hexagonal chip form with a side of 300μm on the semiconductor wafer. The thus formed separation grooves haddepth of about 30 μm and a width of about 10 μm, and the sapphiresubstrate was exposed. The separation grooves possessed a V-shape incross section. After the separation grooves had been formed, the vacuumchuck was released, and the wafer was stripped off the stage. Next, thewafer was set on a stage of the washing machine, and the protection filmwas removed therefrom, by flowing water, while rotating the wafer.

Next, the back surface of the sapphire substrate of the wafer was groundand polished to form a thin plate of a thickness of about 80 μm. Thewafer was divided by the application of stress by using rollers toobtain orthohexagonal chips in a number of about 7000. Those withoutdefective appearance were taken out to obtain an yield of about 80%.

An obtained chip was placed on a lead frame with the sapphire substratebeing on the lower side, and was fixed with an adhesive. The n-electrodewas connected to the first lead frame, and the p-electrode bonding padwas connected to the second lead frame using gold wires, respectively,to pass a device drive current into the chip. Further, the whole bodywas molded with a transparent epoxy resin to obtain an LED lamp. The LEDlamp was measured by using an integrating sphere to find that thelight-emitting output was 7.3 to 8.1 mW with a current of 20 mA.

Example 2

A blue light-emitting device comprising a Group III nitridesemiconductor was fabricated in a manner as described below. The formthereof on a plane was the same as that of Example 1.

A Group III nitride semiconductor stacked layer structure was formed bysuccessively stacking, on a sapphire substrate having a diameter of 5.1cm (2 inches) via a buffer layer of AlN, an underlying layer of undopedGaN having a thickness of about 4 μm, an n-side contact layer ofGe-doped (concentration of 1×10¹⁹/cm³) GaN having a thickness of about 2μm, an n-side clad layer of Ge-doped (concentration of about 1×10¹⁸/cm³)Ino.₁Gao.₉N having a thickness of about 12.5 nm, a light-emitting layerof a multiple quantum well structure, in which a barrier layer of GaNhaving a thickness of about 16 nm and a well layer of In_(0.2)Ga_(0.8)Nhaving a thickness of about 2.5 nm were stacked five times alternatelyand finally the barrier layer was further stacked, a p-side clad layerof Mg-doped (concentration of 1×10²⁰/cm³) Alo.o₇Gao.₉₃N having athickness of about 2.5 nm and a p-side contact layer of Mg-doped(concentration of 8×10¹⁹/cm³) Alo.o₂Gao.98N having a thickness of about0.16 μm by an MOCVD method.

On the p-side contact layer of the Group III nitride semiconductorstacked layer structure, there was formed a light-transmittingp-electrode having a structure of laminating a Pt layer and an Au layersuccessively from the side of the p-side contact layer on apredetermined position relying upon a photolithography technology and alift-off technology. Then, relying upon the photolithography technology,there was formed a p-electrode bonding pad having an Au/Ti/Al/Ti/Aulayer structure from the semiconductor side.

Next, relying upon the photolithography technology and the reactive ionetching technology, the n-type layer was exposed by etching, and asurface for forming n-electrode was formed in a semicircular shape byetching. At the same time, trenches having a side length of about 300 μmand a groove width of about 18 μm were formed in the form oforthohexagonal chips. The trenches were in a honeycomb pattern oforthohexagons over the whole semiconductor wafer. Next, an insulatingfilm of a silicon oxide was formed on a portion where there were exposedan active layer and a p-type layer surrounding the n-electrode formingsurface, and an n-electrode of a Cr/Ti/Au three-layer structure wasformed on the n-electrode forming surface by a method known among peopleskilled in the art.

The thus obtained Group III nitride semiconductor wafer was sent to thestep for cutting. First, a water-soluble resist was uniformly applied byusing a spin coater onto the whole surface on the semiconductor layerside of the wafer, and was dried to form a protection film having athickness of about 0.2 μm so that contaminant due to the cutting willnot adhere onto the Group III nitride semiconductor layer at the time ofmachining with a laser.

Next, a UV tape was stuck to the sapphire substrate side of the waferand was fixed by a vacuum chuck onto a stage of a pulse laser machiningapparatus. The stage was of a rotary structure which was controlled by acomputer to move in the X-axis (right and left) and in the Y-axis (backand forth) directions. After being fixed to the vacuum chuck, a laseroptical system was so adjusted that the focal point of laser was on thesurface of the protection film, and separation grooves were formed inthe bottom of the trench by the irradiation with a laser beam. Theseparation grooves were formed by irradiating the trenches with a laseras shown in FIG. 1 so as to traverse the semiconductor wafer to, first,form a polygonal line (A1) having the same length of sides with an angleof 120 degrees. Next, separation grooves were formed describing apolygonal line (A2) which was a parallel translation of the polygonalline (A1). This was repeated to form separation grooves of the shape ofthe polygonal line over the whole surface of the semiconductor wafer.Next, as shown in FIG. 2, every other bending point of the polygonalline was selected and was connected to a bending point of theneighboring polygonal line which was a parallel translation to formseparation grooves as represented by straight lines (B). Separationgrooves were further formed as represented by straight lines (C) byconnecting the bending points that were not selected to the bendingpoints of a neighboring polygonal line moved in parallel toward theopposite side. Thus, there were formed separation grooves of a honeycombhexagonal chip form with a side of 300 μm on the trenches of thesemiconductor wafer. The thus formed separation grooves possessed adepth of about 25 μm and a width of about 10 μm, and the sapphiresubstrate was exposed. The separation grooves possessed a V-shape incross section. After the separation grooves had been formed, the vacuumchuck was released, and the wafer was stripped off the stage. Next, thewafer was set on a stage of the washing machine, and the protection filmwas removed therefrom, by flowing water, while rotating the wafer.

Next, the back surface side of the sapphire substrate of the wafer wasground to form a thin plate of a thickness of about 80 μm. The wafer wasdivided by the application of stress by using rollers to obtainorthohexagonal chips in a number of about 7000 as shown in FIG. 5. Thosewithout defective appearance were taken out to obtain an yield of about80%.

The obtained chips were molded into LED lamps in the same manner as inExample 1 and were evaluated to find that the light-emitting output was9.3 to 10 mW with a current of 20 mA.

Example 3

In Example 1, the laser beam was irradiated in a manner as describedbelow. Referring to FIG. 4, separation grooves of the same length as thelength of a side of a hexagonal chip form were discretely formed like abroken line in a first direction to form separation grooves (E) of theform of a broken line in the first direction. Next, the stage was turnedby 60 degrees. Separation grooves of the same length as the length ofthe side of the hexagonal chip form were formed like a broken linestarting from the ends of the separation grooves (E) of the form of abroken line in the first direction, thereby to form separation grooves(F) of the form of a broken line in a second direction. Next, the stagewas turned by another 60 degrees. Separation grooves of the same lengthas the length of the side of the hexagonal chip form were formed like abroken line starting from the ends of the separation grooves (F) of theform of a broken line in the second direction, thereby to formseparation grooves (G) in the form of a broken line in a thirddirection. Thus, there were formed separation grooves to give ahoneycomb hexagonal chip form having a side of 300 μm on thesemiconductor wafer. The size of the separation grooves and the formthereof in cross section were nearly the same as those of Example 1. Theobtained chips were molded into LED lamps like in Example 1 and wereevaluated to find that a light-emitting output was 7.3 to 8.1 mW with acurrent of 20 mA.

Example 4

The semiconductor wafer of Example 2 was ground to possess a thicknessof about 80 μm, was placed on a spherical metal mold and was pushedthereon from the upper side so as to be divided into individual chips.The chips without defective appearance were taken out to obtain an yieldof about 85%.

Example 5

Orthohexagonal chips were obtained in a number of about 7000 in the samemanner as in Example 2 but forming a light-reflecting p-electrode havinga structure of laminating a Pt layer and an Rh layer in this order fromthe side of the p-side contact layer. The chips without defectiveappearance were taken out to obtain an yield of about 80%.

The n-electrode and the bonding pad of the p-electrode of the obtainedchip were connected to the negative electrode and the positive electrodeof a sub-mount in which an electric circuit has been incorporated via asolder. The sub-mount was further placed on a lead frame to pass adevice drive current to the chip. Further, the whole body was moldedwith a transparent epoxy resin to obtain an LED lamp. The LED lamp wasmeasured by using an integrating sphere to find that the light-emittingoutput was 19 to 21 mW with a current of 20 mA.

Example 6

The semiconductor wafer of Example 5 was ground and polished to have athickness of about 80 μm. Thereafter, second separation grooves of adepth of about 15 μm and a width of about 20 μm were formed by theirradiation with a laser beam at positions on the polished surface sideof the substrate corresponding to the positions for forming theseparation grooves. The separation grooves possessed nearly a V-shape,and the corners of the substrate were chamfered. The wafer was dividedby the application of stress by using rollers to obtain about 7000orthohexagonal chips. The chips without defective appearance were takenout to find an yield of about 90%.

The obtained chips were molded into LED lamps in the same manner as inExample 5 and were evaluated to find that a light-emitting output was 20to 23 mW with a current of 20 mA.

Example 7

Chips of a pentagonal shape form were obtained in a number of about14,000 in the same manner as in Example 1 with the exception of formingseparation grooves for obtaining pentagonal chips shown in FIG. 6 byforming a separation groove of a straight line (D) shown in FIG. 3 afterformation of separation grooves of the form of straight lines (C) shownin FIG. 2. Chips without defective appearance were taken out to obtainan yield of about 80%.

The obtained chips were molded into LED lamps in the same manner as inExample 1 and were evaluated to find that the light-emitting output was3.5 to 3.8 mW with a current of about 20 mA.

Example 8

A light-emitting device was fabricated according to the same procedureas that of Example 1 but by so forming the separation grooves that thechip possessed a circular shape of a radius of 275 μm. As there existeda region that could not be used as a light-emitting device between thecircles, the effective area for use as the chip was about 80% ascompared to that of the case of the orthohexagonal shape. Referring toFIG. 7, the electrode shape was such that the n-electrode formingsurface (3) was at the central portion of the chip surrounded by thearrangement of p-electrode (1). Circular chips were obtained in a numberof about 6,000 according to the procedure of Example 1. The chipswithout defective appearance were taken out to obtain an yield of about70%.

The obtained chips were molded into LED lamps in the same manner as inExample 1 and were evaluated to find that the light-emitting output was8.1 to 8.3 mW with a current of 20 inA.

INDUSTRIAL APPLICABILITY

The compound semiconductor light-emitting device obtained according tothe present invention exhibits a good current distribution, can beeasily applied even to a large chip, helps improve the light extractionefficiency on the side surfaces of the chip, and offers an increaseddegree of freedom in the arrangement of chips that are mounted,presenting a very great value for the utilization, particularly, in thelighting industries. Besides, the chips can be taken out from thesubstrates maintaining an improved yield and can be produced in largequantities at a decreased cost.

1. A method of producing a Group III nitride semiconductor device havinga chip shape which is a pentagonal or more highly polygonal shape,comprising a first step of epitaxially growing a Group III nitridesemiconductor on a substrate to form a semiconductor wafer; a secondstep of irradiating said semiconductor wafer with a laser beam to formseparation grooves; a third step of grinding and/or polishing the mainsurface side different from the epitaxially grown main surface of thesubstrate; and a fourth step of division into individual chips byapplying stress to said separation grooves, wherein the second stepirradiates the laser beam from the semiconductor side of thesemiconductor wafer, and after the second step, further including afifth step of forming trenches, in which at least the n-type layer isexposed, being corresponded to the positions for forming the separationgrooves.
 2. A method of producing a Group III nitride semiconductordevice according to claim 1, wherein the first step, the second step,the third step and the fourth step are included in this order.
 3. Amethod of producing a Group III nitride semiconductor device accordingto claim 1, wherein the separation grooves are at least partly reachingthe substrate.
 4. A method of producing a Group III nitridesemiconductor device according to claim 1, wherein the second stepcomprises a step of irradiating a laser beam from the semiconductor sideof the semiconductor wafer and a step of irradiating a laser beam fromthe substrate side of the semiconductor wafer.
 5. A method of producinga Group III nitride semiconductor device according to claim 1, whereinthe separation grooves have a V-shape in the cross section.
 6. A methodof producing a Group III nitride semiconductor device according to claim1, wherein the thickness of the semiconductor wafer is ground and/orpolished at the third step to be not larger than 150 μm.
 7. A method ofproducing a Group III nitride semiconductor device according to claim 1,wherein the fourth step is executed by pushing the substrate onto aspherical metal mold.
 8. A method of producing a Group III nitridesemiconductor device according to claim 1, wherein the chip shape issubstantially an orthohexagonal shape.
 9. A method of producing a GroupIII nitride semiconductor device according to claim 1, wherein the chipshape is substantially a pentagonal shape.
 10. A method of producing aGroup III nitride semiconductor device according to claim 1, wherein thechip is substantially of a circular form.
 11. A method of producing aGroup III nitride semiconductor device according to claim 1, wherein theGroup III nitride semiconductor device is a light-emitting device.
 12. Amethod of producing a Group III nitride semiconductor device accordingto claim 11, wherein the first step forms the semiconductor wafer byepitaxially growing an n-type layer, a light-emitting layer and a p-typelayer comprising the Group III nitride semiconductor in this order onthe substrate.
 13. A method of producing a Group III nitridesemiconductor device having a chip shape which is a pentagonal or morehighly polygonal shape, comprising a first step of epitaxially growing aGroup III nitride semiconductor on a substrate to form a semiconductorwafer; a second step of irradiating said semiconductor wafer with alaser beam to form separation grooves; a third step of grinding and/orpolishing the main surface side different from the epitaxially grownmain surface of the substrate; and a fourth step of division intoindividual chips by applying stress to said separation grooves, whereinthe second step forms a separation groove of the form of a polygonalline that is bent, forms a plurality of separation grooves of the formof a polygonal line that is bent in a form of being translated inparallel and, then, forms linear separation grooves by connecting everyother bending points of the neighboring separation grooves of the formof a polygonal line.
 14. A method of producing a Group III nitridesemiconductor device having a chip shape which is a pentagonal or morehighly polygonal shape, comprising a first step of epitaxially growing aGroup III nitride semiconductor on a substrate to form a semiconductorwafer; a second step of irradiating said semiconductor wafer with alaser beam to form separation grooves; a third step of grinding and/orpolishing the main surface side different from the epitaxially grownmain surface of the substrate; and a fourth step of division intoindividual chips by applying stress to said separation grooves, whereinthe second step forms first separation grooves of the form of a brokenline, forms second separation grooves of the form of a broken line thatintersect the first separation grooves of the form of the broken line ata first angle, and forms third separation grooves of the form of abroken line that intersect the second separation grooves of the form ofthe broken line at a second angle and further intersect the firstseparation grooves of the form of the broken line at a third angle, thesum of the first angle, the second angle and the third angle being 180degrees.
 15. A method of producing a Group III nitride semiconductordevice having a chip shape which is a pentagonal or more highlypolygonal shape, comprising a first step of epitaxially growing a GroupIII nitride semiconductor on a substrate to form a semiconductor wafer;a second step of irradiating said semiconductor wafer with a laser beamto form separation grooves; a third step of grinding and/or polishingthe main surface side different from the epitaxially grown main surfaceof the substrate; and a fourth step of division into individual chips byapplying stress to said separation grooves, wherein the chip shape issubstantially a pentagonal shape and the second step forms separationgrooves of the hexagonal shape by forming separation grooves of the formof a polygonal line that is bent, forming separation grooves of the formof a plurality of polygonal lines that are bent in a form of beingtranslated in parallel and, then, forming linear separation grooves byconnecting every other bending points of the neighboring separationgrooves of the form of polygonal lines and, further, forms linearseparation grooves connecting the opposing two sides of the separationgrooves of said hexagonal form.
 16. A method of producing a Group IIInitride semiconductor device having a chip shape which is a pentagonalor more highly polygonal shape, comprising a first step of epitaxiallygrowing a Group III nitride semiconductor on a substrate to form asemiconductor wafer; a second step of irradiating said semiconductorwafer with a laser beam to form separation grooves; a third step ofgrinding and/or polishing the main surface side different from theepitaxially grown main surface of the substrate; and a fourth step ofdivision into individual chips by applying stress to said separationgrooves, wherein the chip shape is substantially a pentagonal shape andthe second step forms separation grooves of the form of the hexagonalshape by forming first separation grooves of the form of a broken line,forming second separation grooves of the form of a broken line thatintersect the first separation grooves of the form of the broken line ata first angle, and forming third separation grooves of the form of abroken line that intersect the second separation grooves of the form ofthe broken line at a second angle and further intersect the firstseparation grooves of the form of the broken line at a third angle, thesum of the first angle, the second angle and the third angle being 180degrees and, further, forms linear separation grooves connecting theopposing two sides of the separation grooves of said hexagonal form.